A variety of closed circuit breathing devices has previously been developed for use in a variety of applications, including hazardous work areas such as deep shaft mines. These devices are known as self-contained self-rescuer (SCSR) units. They typically provide an oxygen supply for breathing for up to one hour to give a miner time to escape conditions where there are toxic fumes present in the mine.
In previously available SCSR units, the need for extended service was balanced with portability. The desired one hour of breathable air has been provided with compressed oxygen or air supplies or oxygen generation systems, generally in combination with a carbon dioxide absorbent. Such systems often have the components included in canisters or tanks. High pressure tanks, in turn, require heavy pressure regulators to step down the high pressure of the compressed gas to the low pressure required for breathing bag inflation. Moreover, previous regulator systems relied on manual operation for adjustment of the flow of gas from the pressure tanks to the user.
In addition to the problem of overall bulk and weight of previously available regulator systems, the efficiency of known regulators did not maximize the use of available breathable gas.